Contents

Abstract

"The BioBoard" is an Arduino-controlled sensor package that allowusers to monitor a range of physiochemical factors related to microbiological processes (e.g. algae growing, youghurt production, kombucha fermentation, sourdough culturing, etc.) in liquid media/cultures, with real-time wireless data transmission and graphic data visualization designed to make key correlations between these factors easily graspable.

Goals / Features

As a minimum, we want to be able to monitor temperature, pH and dissolved oxygen. We'd also like to be able to measure biomass, either directly or by proxy. The current plan is to build a thermometer, a dissolved oxygen sensor and a biomass probe ourselves, and supplementing with a commercial pH meter. Failing that, we'll buy a thermometer and an oxygen probe as well and attempt to hack them instead, and concentrate on standardising data protocols, building the supporting controller hardware and making the graphics look pretty.

Hardware

Sensors

Important considerations are affordability, accessibility and required precision.

Charlie has access to a good amount of Type K metal sheathed TC wire, plus assorted probes and a TC reader he can donate - as we go along our improving expertise will lead us to resources other people can use... like the relatively cheap McMaster Carr wire.

We presently have a not-quite-functional prototype digital thermometer which uses a DS18B20 DTS; the sketch is compiling correctly, but there's de-bugging to be done (error msg reads: avrdude: stk500_getsync(): not in sync: resp=0x31).

Dissolved oxygen (DO) probes

Membrane electrode (a.k.a. strip an automotive O2 sensor for parts to make a membrane electrode)

Pros

New sensors for out of date cars are available on eBay for $10

Contain required platinum, anodes, and teflon membrane

Cons

Sensors typically operate at ~300C

Progress

Ordered 3 $6-$10 probes on ebay to futz with

Plan is to knock out the zirconium matrix and add a KCl electrolyte to see if we can get a reaction started at room temperature.

Optode (a.k.a. build an intensity- or time-based optode from scratch)

Recently, people have been using a ruthenium complex as a visual (fluorescent) indicator of oxygen concentration. This complex is excited by a blue LED, then its transmission is measured by a filtered photoresistor (more details here in pdf)

Industry has commercial probes available which measure living biomass; we think we may be able to retroengineer such a thing. With enough calibration, it might be possible to do this by measuring capacitance alone.

[The basic principle behind these probes is the different electrical properties of living and dead cells; both are conductive - being essential very long and folded chains of carbon molecules - but living cells also act as capacitors (batteries); active transport across the cell membrane of electrically charged ions/molecules establishes a negative potential/charge on the order of -70mV in resting mammalian neurons.]

Other resources

[finesse.com/files/pdfs/app-tech-notes/TruCell.TN.AUvsOD.pdf .pdf with technical notes about a commercial OD probe]

Software

Data logging and visualization

Include "export to CSV" function with option for data set selection - should allow people to use a variety of programming languages and data analysis tools without a lot of work on their part or ours

Web server

Custom Rails app

Receives data

Logs to database

Generates graphs on demand

Add Comet server for live-updated graphs

Include 'export to CSV' function to allow users to extract data for analysis with tool(s)

All code on github so others can fork and add features

We could add features that lets new users sign up and get a unique key which they use when transmitting their own data to the JSON web service on our server. The server then uses the key to associate the data with the user, and the user can look at their graphs and share them with others.